The World’s First Omnivorous Shark – The Bonnethead

According to recent study, researches have found the first omnivorous shark that we know of. The bonnet head shark enjoys a diet of bony fish, crabs, snails, shrimp and sea-grass.

Biologists have long been observing that bonnetheads ingest sea grass along with their favorite crustaceans and shellfish. However because their stomach is almost identical to a meat-eating shark, scientists had always assumed the sea grass was eaten by accident.

But after careful study by Samantha Leigh and her colleagues at the University of California Irvine, it has been discovered that bonnetheads enjoy seagrass, which they consume for its nutritional value. The study also ran a series to determine how much of this seagrass diet could be digested.

First, in the Florida Bay lab seagrass was planted. Researchers then added carbon isotope to the water in order to track the plants along the food chain that would eventually reach the sharks.

A total of five bonnetheads were served a diet made up of 10% squid and 90% seagrass in a controlled environment in the lab. Three weeks later the sharks could have been seen to have put on weight from the consuming calories from the plant-based diet.

In order to be crystal clear, researches ran a new series of tests which involved measuring how much of the plant matter was digested and how much of it simply passed through.

Finally, Leigh and her colleagues found the types of digestive enzymes that break down the plant-based food. Other sharks who eat meat have very low levels of enzymes that break down fibers and carbs. The bonnethead had a high levels of these types of enzymes. More than half of the organic matter found in seagrass was digested by the bonnetheads.

“Bonnethead sharks are not only consuming copious amount of seagrass but they are actually capable of digesting and assimilating seagrass nutrients, making them clear omnivores,” the researchers wrote in their study.

“This is the first species of shark ever to be shown to have an omnivorous digestive strategy.”